Fix install adb reboot assert method.

Author: vhristov5555

core/device/helpers/adb.py

@@ -405,5 +405,5 @@ def reboot_device(device_id):
         """
         command = 'reboot'
         output = Adb.run(command=command, device_id=device_id)
-        assert 'Events injected: 1' in output, 'Failed to start reboot.'
+        assert '' in output, 'Failed to reboot the device.Error:' + output
         print 'Reboot started successfully.'